The present invention is directed to the fabrication of thermal insulation of selected configurations from zirconia fibers, and more particularly to such a thermal insulation wherein the zirconia fibers are joined in a matrix of zirconia at their nexi to form a rigid configured structure.
Furnaces for various metallurgical procedures require operating temperatures up to about 2,000.degree. C. Such high furnace temperatures require the use of a thermal insulation which possess several properties not commonly found in most thermal insulations. For example, the insulation must be capable of withstanding the high furnace temperatures without degradation while protecting furnace components from the intense heat.
A thermal insulation found satisfactory for use in such high temperature furnaces is formed of yttria stabilized zirconia fibers which possess an extremely high melting point exceeded only by oxides of hafnium and thorium. Efforts to utilize thermal insulation formed of zirconia fibers have been somewhat limited due to the fact that commercially available zirconia-fiber thermal insulation can not be readily shaped to fit particular configurations within the furnace and is available only in the form of flat boards or blocks of various thicknesses. These blocks or boards are somewhat friable and readily fall apart when subjected to stresses such as occur during machining and the like. Further, the fibrous zirconia insulation which is capable of use at temperatures as high as 2,000.degree. C. must be held together in a supporting framework in order to maintain structural integrity. A configured form of zirconia fiber thermal insulation is available, but this pre-configured zirconia insulation requires the use of a silica binder for holding the zirconia fibers together. The presence of the silica forms an impurity or residue in the final structure which lowers the maximum service temperature to about 1,650.degree. C.
Thus, there is a significant need for zirconia thermal insulation capable of withstanding 2,000.degree. C. temperatures that is self supporting and which can be shaped into desired self-supporting configurations.